TextPad
is free to evaluate (with periodic "nag" screens). It
is $27 to purchase.

With
a custom syntax definition file (.syn) and clip library (.tcl) for the Zillions language
ZRF syntax is highlighted as shown above; the text clips on the left are easily inserted
into the script.
The syntax definition file was written
by Kevin Crocker and modified by Jeff Mallett.

Control-M
and Control-Shift-M are useful for matching parentheses.

To
install the syntax definition file and clip library into your copy of TextPad: